Methods for synchronized pulse shape tailoring

ABSTRACT

A plurality of subresonators ( 12, 14 ), having different design configurations, share a common resonator section ( 18 ) such that the lasing action can be substantially synchronized to provide coherent laser pulses that merge the different respective pulse energy profile and/or pulse width characteristics imparted by the configurations of the subresonators ( 12, 14 ). The subresonators ( 12, 14 ) may share a laser medium ( 42 ) in the common section, or each distinct subresonator section ( 28, 36 ) may have its own laser medium ( 42 ). Exemplary long and short subresonators ( 12, 14 ) generate specially tailored laser pulses having a short rise time and a long pulse width at one wavelength or two different wavelengths that may be beneficial for a variety of laser and micromachining applications including memory link processing.

Related Applications

This patent application claims benefit of U.S. Provisional ApplicationNo. 60/635,053, filed Dec. 9, 2004.

COPYRIGHT NOTICE

© 2005 Electro Scientific Industries, Inc. A portion of the disclosureof this patent document contains material that is subject to copyrightprotection. The copyright owner has no objection to the facsimilereproduction by anyone of the patent document or the patent disclosure,as it appears in the Patent and Trademark Office patent file or records,but otherwise reserves all copyright rights whatsoever. 37 CFR § 1.71(d).

TECHNICAL FIELD

Controlling laser pulse width and/or power profile can be enhanced byemploying a laser having two or more subresonators that share a commonsection.

BACKGROUND OF THE INVENTION

Diode-pumped (DP), solid-state (SS) lasers running at high pulserepetition rates are employed widely in a variety of applicationsincluding laser micromachining. In these lasers, the pulse width islargely determined by the resonator design and affected by laser pumpinglevel and pulse repetition rate for a given laser medium. Once theresonator is constructed, there are few practical ways for changing thepulse width or temporal power profile for a given laser medium at agiven pumping level and pulse repetition rate. However, for someapplications such as processing links, particularly in stacks, bettercontrol of the pulse width and temporal energy profile while maintainingother laser pulse parameters is desirable.

Lasers employing a fast diode master oscillator/fiber amplifier (MOPA)configuration can deliver substantially square energy profile laserpulses with an adjustable pulse width of about 1 ns-10 ns, but currentfiber amplifiers deliver random unpolarized laser output and typicallyhave a disadvantageous wider wavelength spectrum output that imposespractical difficulties in achieving focused beam spot sizes that aresufficiently small to perform the desired micromachining operationswithout adversely affecting nearby substrates or other materials. U.S.patent application Ser. Nos. 10/921,481 and 10/921,765 of Sun et al.,which are assigned to the assignee of this patent application, describeways to obtain MOPA pulses with energy profiles that are speciallytailored to particular applications.

Electro-optic (E-O) devices can also be employed as optical gates toreshape the energy profile or pulse width of laser pulses. However,operating the E-O devices at high repetition rates, especially aboveabout 40 kHz, and synchronizing the laser pulses and the action(s) of anE-O device to a desired accuracy are extremely difficult to achieveunder practical constraints.

Laser pulses emitted by two independent lasers that generate pulseshaving respectively different temporal energy profiles and pulse widthscan be theoretically combined to provide a combined energy profile andpulse width of desirable features. However, in practice, combinations ofsuch independently produced pulses suffer from laser pulse jitter, whichis a random fluctuation of laser pulse initiation relative to laserpulse initiation control signals that is inherent to typical Q-switchedlasers. In many applications, the pulse jitter is often greater than 5ns-30 ns, depending on the laser design and the laser pulse repetitionrate. This jitter is often too large to facilitate pulse combinationwith desirable accuracy, especially when the sets of combined pulses aredesired to occur at intervals of less than 200 ns. For example,consistent and reproducible pulse energy profiles for an applicationlike laser link processing could demand a timing stability between thetwo pulses of better than 1 ns. This synchronization problem becomesmore significant at high repetition rates, especially above about 40kHz, for example.

SUMMARY OF THE INVENTION

An object of some embodiments is to provide a laser and/or method forcontrolling the energy profile and/or pulse width of a laser pulse.

One embodiment of the invention employs two or more subresonators thatshare a common resonator section such that the lasing action issubstantially self-synchronized. Each subresonator has a differentdesign configuration, such as subresonator length, that is adapted toprovide at least one different pulse energy profile and/or pulse widthcharacteristic. When the shared part of the resonator includes theoutput port, the resulting laser output provides unique laser outputpulses that merge energy profile and/or pulse width characteristicsimparted by the configurations of the subresonators. In someembodiments, the subresonators share a laser medium in the commonresonator section; and in some embodiments, each subresonator sectionmay have its own laser medium. In one embodiment, long and shortsubresonators share a common resonator section to generate laser pulseshaving a short rise time and a long pulse width.

In some embodiments, the common resonator section includes a highreflectivity mirror, while each subresonator section has its own outputport. The laser profile characteristics from each subresonator can thenbe recombined outside of the resonator while many of the adverseconsequences of laser pulse jittering may be significantly reduced. Thedistinct profiles of the subsresonator outputs can be subjected todifferent optional harmonic conversion techniques before the profilesare recombined into a laser output pulse, permitting the laser outputpulse to have a specially tailored profile using more than one laserwavelength. In other embodiments, such different wavelength profiles canbe controlled to occur at different times with respect to each other.

Additional aspects and advantages will be apparent from the followingdetailed description of preferred embodiments, which proceeds withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a laser composed of two subresonatorshaving a common resonator section that includes a laser medium and anoutput port.

FIG. 2A is a schematic diagram of a laser composed of two subresonators,each of which includes a laser medium, that share a common resonatorsection in which no a laser medium is housed.

FIG. 2B is a schematic diagram of an alternative laser composed of twosubresonators, each of which includes a laser medium and an AOM, thatshare a common resonator section in which no a laser medium is housed.

FIG. 3A is a schematic diagram of a laser composed of two subresonators,each of which includes a laser medium and an output port, that share acommon resonator section with a high reflectivity mirror.

FIG. 3B is a schematic diagram of an alternative laser composed of twosubresonators, each of which includes a laser medium, an AOM, and anoutput port, that share a common resonator section with a highreflectivity mirror.

FIGS. 4A-4C show power versus time graphs of respective shortsubresonator profiles, long subresonator profiles, and speciallytailored profiles of the resulting output pulses.

FIGS. 5A-5C show power versus time graphs of respective shortsubresonator profiles, long subresonator profiles, and speciallytailored profiles of the resulting output pulses when a first exemplarytime delay is employed.

FIGS. 6A-6C show power versus time graphs of respective shortsubresonator profiles, long subresonator profiles, and speciallytailored profiles of the resulting output pulses when a second exemplarytime delay is employed.

FIGS. 7A-7C show power versus time graphs of respective shortsubresonator profiles, long subresonator profiles, and speciallytailored profiles of the resulting output pulses when a third exemplarytime delay is employed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic diagram of a laser 10 having a long subresonator12 and a short subresonator 14 that are integrated with a beamsplitter16 to employ a common resonator section 18. The beamsplitter 16 may be amirror that is partly reflective and transmissive to permit oscillationto be established substantially simultaneously in both the longsubresonator 12 and the short subresonator 14. The beamsplilter 16 mayalternatively be a polarizer which will allow the oscillation of asubstantially p-polarized laser beam in the short subresonator 14 and asubstantially s-polarized laser beam in the long subresonator 12.

With reference to FIG. 1, the long subresonator 12 is defined by a longsubresonator mirror 22 and an output port 24 that are positioned alongan optical path 26. The long subresonator 12 includes the commonresonator section 18 and a long subresonator section 28. The shortsubresonator 14 can be defined by a short subresonator mirror 34 and theoutput port 24 and, therefore, includes the common resonator section 18and a short subresonator section 36. Laser 10 may also employ anoptional loss reduction subsection 38 with a loss reduction mirror 40.The long subresonator mirror 22, the short subresonator mirror 34, andthe optional loss reduction mirror 40 are preferably all highlyreflective (HR) to the desired wavelength produced by a laser medium 42that is positioned in the common resonator section 18.

The laser medium 42 preferably comprises a conventional solid-statelasant such as Nd:YAG, Nd:YLF, Nd:YVO₄, or Yb:YAG, making available allof their typical laser wavelengths as well as the harmonics thereof. Insome embodiments, the laser medium 42 is directly or indirectly pumpedfrom the side by one or more diodes or diode arrays (not shown). Skilledpersons will, however, appreciate that the pumping source could bepositioned behind one or more of the long resonator mirror 22, the shortresonator mirror 34, or the optional loss reduction mirror 40 if theyare properly adapted to be input couplers at the desired pumpingwavelength. Other well-known optical components (not shown) couldadditionally or alternatively be employed to facilitate end-pumping.Skilled persons will also appreciate that one or more lamps, lasers, orother pumping devices could be employed to provide the pumping light andthat the laser medium 42 could alternatively employ a different type oflaser medium such as a gas, CO₂, excimer, or copper vapor laser medium.

The common resonator section 18 also preferably includes a Q-switch 44,such as an acousto-optic modulator (AOM) or an electro-optic modulator(EOM), positioned along the optical path 26. An aperture 48 may also beincluded in the common resonator section 18 and may preferably bepositioned between the laser medium 42 or Q-switch 44 and the outputport 24. The output port 24 is preferably an output coupling mirror thatis partly reflective (PT) (about 5%-20% transmissive) to the preferredwavelength generated by the laser medium 42.

Exemplary laser output repetition rates are greater than about 1 Hz,greater than about 1 kHz, greater than about 25 kHz, greater than about40 kHz, or greater than about 100 kHz and up to about or greater than500 kHz. In typical embodiments, other pulse parameters include, but arenot limited to, a laser energy of 0.1 μJ to 10 μJ and even up to 100 mJat a laser output repetition rate from about 1 Hz up to about 500 kHz.

If desirable, one or more wavelength converters 52 can be positionedalong the optical path 26 outside of the common resonator section 18 toconvert the laser output 50 a to harmonic laser output. Each wavelengthconverter 52 preferably comprises one or more nonlinear crystals, suchas KTP (potassium titanium oxide phosphate, KTiOPO₄), BBO (beta bariumborate, beta-BaB₂O₄), and LBO (lithium triborate, LiB₃O₅), for laserwavelength conversion. Typical fundamental laser wavelengths include,but are not limited to, 1064 nm, which has harmonic wavelengths at 532nm (frequency doubled), 355 nm (frequency tripled), 266 nm (frequencyquadrupled), and 213 nm (frequency quintupled). Skilled persons willappreciate that the wavelength converters 52 could alternatively beplaced within the common resonator section 18 for intra-cavity frequencyconversion.

Because the short subresonator 14 and the long subresonator 12 share thecommon resonator section 18, the laser energy and lasing action in bothsubresonators 12 and 14 is coupled. This coupling of laser action mayresemble injection seeding from one subresonator to the othersubresonator, so the lasing actions of the two (or more) subresonatorsare substantially self-synchronized into a single lasing pulse with highprofile stability.

FIG. 2A is a schematic diagram of a laser 80 a having a longsubresonator 82 a and a short subresonator 84 a that are integrated witha beamsplitter 16 to employ a common resonator section 88 a. The commonresonator section 88 a is in optical association with a longsubresonator section 92 a to form the long subresonator 82 a, and thecommon resonator section 88 a is in optical association with a shortsubresonator section 94 a to form the short subresonator 84 a. The laser80 a of FIG. 2A is very similar to the laser 10 of FIG. 1, so many oftheir corresponding components are similarly labeled.

One significant difference in laser 80 is that the long subresonatorsection 92 a contains a laser medium 42 a and the short subresonatorsection 94 a contains a laser medium 42 b to permit more versatility inthe energy profiles 160 (FIGS. 4-7) of pulses of laser output 50 b ₁. Inmost embodiments, laser media 42 a and 42 b preferably comprise the samelasant, but skilled persons will appreciate that laser medium 42 a couldbe different from laser medium 42 b in, for example, composition, size,configuration, or dopant concentration as long as their lasingwavelengths are substantially similar. In one embodiment, laser medium42 a has a rod, disk, rectangular parallelepiped, cube, chip, slab, orother shape, and laser medium 42 b has a different one of these shapes.

In some preferred embodiments, laser media 42 a and 42 b are pumped withthe same pumping coupling methods, by the same pumping sources, and atthe same pumping levels and timing schemes through the use ofconventionally known drive electronics. For some applications, such aslink severing, CW pumping is generally preferred. In other embodiments,laser media 42 a and 42 b are pumped with different pumping couplingmethods, by different pumping sources, and/or at different pumpinglevels and timing schemes through the use of conventionally known driveelectronics. In some embodiments, for example, laser medium 42 a can beend pumped while laser medium 42 b is side pumped, or vice versa.

Although the common resonator section 88 a could also contain a lasermedium 42, such an embodiment is less preferred. An optional polarizer90 may be employed in both the long subresonator section 92 a and theshort subresonator section 94 a, but is shown positioned within the longsubresonator section 92 a as an example.

FIG. 2B is a schematic diagram of an alternative laser 80 b that is verysimilar to laser 80 a, so many of their corresponding components aresimilarly labeled. One significant difference in laser 80 a is that thecommon Q-switch 44 is removed from the common resonator section 88 b,and two independent Q-switches 44 a and 44 b (such as AOMs) are insertedinto the long and short subresonator sections 92 b and 94 b,respectively. The Q-switches 44 a and 44 b can be initiated at the sametime by a single driver (such as an RF driver, not shown) or by separatebut synchronized independent drivers.

Alternatively, the Q-switches 44 a and 44 b can be initiated atdifferent times by separate independent drivers to further enhance thetailoring capability of the profile 160 of the pulses of laser output 50b ₂. To ensure the laser energy coupling between the two subresonators82 b and 84 b, skilled persons will appreciate that the delay timebetween the initiation of the Q-switches 44 a and 44 b should be limitedsuch that the later initiated Q-switch should be initiated before thelasing action stops in the subresonator housing the other Q-switch.Although the polarizer 90 is not shown in FIG. 2B, a polarizer can beused in one or more of subresonator sections 92 b and 94 b and/or incommon resonator section 88 b.

FIG. 3A is a schematic diagram of a laser 110 a having a longsubresonator 112 a and a short subresonator 114 a that are integratedwith a beamsplitter 16 to employ a common resonator section 118 a. Thecommon resonator section 118 a is in optical association with a longsubresonator section 122 a to form the long subresonator 112 a, and thecommon resonator section 118 a is in optical association with a shortsubresonator section 124 a to form the short subresonator 114 a. Thelaser 110 a of FIG. 3A is very similar to the laser 80 a of FIG. 2A, somany of their corresponding components are similarly labeled. Onesignificant difference between these lasers is that in the laser 110 athe output port 24 is replaced with a highly reflective mirror 116 andthe long and short subresonator mirrors 22 and 34 are replaced withshort and long output ports 24 c and 24 d to provide distinct buttemporally synchronized profiles 150 and 152 (FIGS. 4-7) of laser output50 c ₁ and 50 d ₁ respectively. One or more additional or alternativeapertures 48 may be included in the subresonator sections 122 a and 124a between the laser media 42 c and 42 d and the respective output ports24 c and 24 d.

Skilled persons will appreciate that, regardless of whether the profiles150 and 152 of laser outputs 50 c ₁ and 50 d ₁ are recombined, theseprofiles 150 and 152 can be considered to form a single temporal pulsehaving specially tailored energy profile characteristics because theprofiles 150 and 152 are temporally joined by the common resonatorsection with high timing accuracy. The laser outputs 50 c ₁ and 50 d ₁can be directed and recombined through conventional optics, such asmirrors 130 and combiner 132, to provide synchronized laser output 50 e₁ having specially tailored pulses. Alternatively, the laser outputs 50c ₁ and 50 d ₁ can be used independently to provide a specially tailoredsynchronized pulse with different energy profile portions impingingseparate targets or target positions.

The laser outputs 50 c and 50 d may also be passed through optionalwavelength converters 52 c and 52 d respectively, which may impart thesame or different wavelength conversions. In one example, the laseroutput 50 c is converted to a second harmonic wavelength and the laseroutput 50 d is converted to a fourth harmonic wavelength. Such laseroutputs 50 c ₁ and 50 d ₁ can be recombined to provide speciallytailored pulses of laser output 50 e ₁ such that each pulse contains twoor more selected wavelengths.

FIG. 3B is a schematic diagram of an alternative laser 110 b that isvery similar to laser 110 a shown in FIG. 3A, so many of theircorresponding components are similarly labeled. One significantdifference in laser 110 b is that the common Q-switch 44 is removed fromthe common resonator section 118 b, and two independent Q-switches 44 aand 44 b (such as AOMs) are inserted into the long and shortsubresonator sections 122 b and 124 b, respectively. The Q-switches 44 aand 44 b can be initiated at the same time by a single driver (such asan RF driver, not shown) or by separate but synchronized independentdrivers.

The Q-switches 44 a and 44 b can be initiated at different times byseparate independent drivers to further enhance the tailoring capabilityof the profile 160 of the pulses of laser output 50 e ₂. In someembodiments, the delay time between the initiation of the Q-switches 44a and 44 b (or vice versa) can be limited such that the later initiatedQ-switch can be initiated before the lasing action stops in thesubresonator housing the other Q-switch to further facilitate laserenergy coupling between the two subresonators 112 b and 114 b.

The pulses of laser output 50 a, 50 b ₁, 50 b ₂, 50 c ₁, 50 c ₂, 50 d ₁,50 d ₂, 50 e ₁, and 50 e ₂ (generically laser output 50) as provided byany of the exemplary embodiments are preferably directed by a beamdelivery system toward respective targets that may also be moved by atarget positioning system. The beam delivery system may include avariety of optional conventional optical components, such as a beamexpander, mirrors, and a focusing lens to produce a focused spot size.For link processing, the focused laser spot diameter is typically withinthe range of between about 0.5 μm and about 3 μm and preferably 40% to100% larger than the width of the link, depending on the link width,link pitch size, link material and other link structure and processconsiderations. For other laser applications, the laser spot size can beadjusted from a few tenths of a micron to a few hundred microns to suitthe application requirements.

A preferred beam delivery and positioning system is described in detailin U.S. Pat. No. 4,532,402 of Overbeck for Method and Apparatus forPositioning a Focused Beam on an Integrated Circuit. Such positioningsystem may alternatively or additionally employ the improvements or beampositioners described in U.S. Pat. No. 5,751,585 of Cutler et al., U.S.Pat. No. 6,430,465 B2 of Cutler, U.S. Pat. No. 6,816,294 of Unrath etal., and/or U.S. Pat. No. 6,706,999 of Barrett et al., which areassigned to the assignee of this patent application. Other fixed-headsystems, fast positioner-head systems such as galvanometer-,piezoelectric-, or voice coil- controlled mirrors, or linearmotor-driven conventional positioning systems or those employed in the5300, 9300, or 9000 model series manufactured by Electro ScientificIndustries, Inc. (ESI) of Portland, Oregon could also be employed.

Because the whole duration of each lasing pulse is shorter than 1,000ns, (typically shorter than 300-500 ns), a typical link processingpositioning system may move a laser spot position less than about 0.1 μm(a distance that is shorter than the link width) within such 1,000 nsperiod. So, the laser system can process links on-the-fly, i.e. thepositioning system does not have to stop moving when the laser systemfires a lasing pulse. In some embodiments, the laser spot of the longand short subresonator profiles encompasses the link width, regardlessof when the spike or peak is positioned.

With reference again to FIGS. 1-3, the characteristics of the longsubresonators 12, 82 a, 82 b, 112 a, and 112 b (generically longsubresonator 12) and the short subresonators 14, 84 a, 84 b, 114 a, and114 b (generically short subresonator 14) are different andindependently selected to provide desired characteristics to the laseroutput 50. In one embodiment, the lengths of the long resonators 12 andthe short resonators 14 are selected to impart particular pulse profilecharacteristics to the laser outputs 50. In particular, the lengths ofthe short subresonator sections 36, 94 a, 94 b, 124 a, and 124 b(generically short subresonator section 36) are adjusted to cooperatewith the lengths of the respective common resonator sections 18, 88 a,88 b, 118 a, and 118 b (generically common resonator section 18) toimpart a short duration rising edge to the pulses of laser output 50,and the lengths of the long subresonator sections 28, 92 a, 92 b, 122 a,and 122 b (generically long subresonator section 28) are adjusted tocooperate with the lengths of the respective common resonator sections18 to impart a long pulse width to the pulses of laser outputs 50. Theparticular values of these pulse characteristics can be independentlyselected, and then the lengths or other characteristics of the shortsubresonator sections 36, long subresonator sections 28, and commonresonator sections 18 can be selected in cooperation with other laserparameters to achieve the desired pulse profile of laser outputs 50.

The relationship between resonator characteristics and pulse profile isrelatively complex. However, for a given laser gain factor with givenpumping energy, the pulse width is generally dependent upon the numberof “round trips” the photons make between the resonator end mirrorsduring the lasing period. Thus, for a particular laser operated undersimilar parameters having a given laser medium 42, a given pumpinglevel, and a given pulse repetition rate, the pulse width is generallydirectly proportional to the cavity length. So, generally, the shorterthe cavity, the shorter the pulse width; and the longer the cavity, thelonger the pulse width. In a link processing example, a typical Nd:YAGlaser with a resonator of 8-10 cm long that is pumped by a 3 W diode hasa pulse width of about 10 ns at 20 kHz. So, by keeping the otherparameters generally the same and selectively shortening the resonator,one can obtain a 5 ns pulse width, or by selectively lengthening theresonator, one can obtain a 20 ns pulse width, for example. In addition,the rise time is affected by the pulse width. The rise time willgenerally be close to the full width at half the maximum peak power (thetime between the points of the pulse profile at its half maximum power).So a shorter pulse width results when a shorter rise time is prescribed.

The components of each subresonator can, therefore, be tailored byskilled practitioners to facilitate generation of its independent pulsepropagation characteristics in accordance with known techniques. Forexample, the placement and curvature of the highly reflective mirrors,the curvature of the surface and length of the laser medium 42, and thepumping and doping level may all be adjusted to make certain propagationcharacteristics from the two conjoined subresonators sufficientlysimilar so that they produce an aligned and substantially similar spotsize on the surface of a workpiece. Alternatively, the components ofeach subresonator can be tailored so that certain propagationcharacteristics, such as spot size for example, are intentionallydifferent. The transmissivity of the output couplers can also beadjusted to affect the pulse duration. With greater transmissivitydecreasing the pulse width and lesser transmissivity increasing pulsewidth.

Link processing with specially tailored pulse shapes derived from thelasers described herein offers a wider processing window and a superiorquality of severed links than does conventional link processing withoutsacrificing throughput. The versatility of laser output pulses permitsbetter tailoring to particular link characteristics or other laserprocessing operations.

FIGS. 4A-4C (collectively, FIG. 4) show power versus time graphs ofrespective virtual short subresonator profiles 150 and long subresonatorprofiles 152, and exemplary specially tailored profiles 160 a. Shortsubresonator profiles 150 and long subresonator profiles 152 are virtualin the sense that they could represent what each subresontor wouldprovide independently if not coupled, but such short subresonatorprofiles 150 and long subresonator profiles 152 wouldn't really existseparately in many of the exemplary embodiments, such as those presentedin FIGS. 1, 2A, and 2B.

With reference to FIG. 4A, for some embodiments, short subresonatorsections 36 are adapted to provide short subresonator profiles 150 witha short pulse width of an exemplary 2 ns-15 ns and a rise time of lessthan about 8 ns and preferably less than about 5 ns. Skilled personswill appreciate that a variety of subranges or alternative ranges forthe pulse width and rise time of such short subresonator profiles 150are possible. One exemplary alternative range includes a pulse width ofless than 10 ns and a rise time of less than 2 ns.

With reference to FIG. 4B, for some embodiments, long subresonatorsections 28 are adapted to provide long subresonator profiles 152 with along pulse width of greater 10 ns and preferably having an exemplarypulse width of 15 ns-50 ns and a rise time that is longer than 5 ns andtypically longer than 8 ns or 10 ns. Skilled persons will appreciatethat a variety of alternative ranges for the pulse width and rise timeof such long subresonator profiles 152 are possible. Some exemplaryalternative ranges include a pulse width of 15 ns-30 ns or a pulse widthgreater than 20 ns.

With reference to FIG. 4C, power profiles 160 exhibit a speciallytailored energy profile that includes spike, rise time, and pulse widthcharacteristics derived from the virtual short subresonator profiles 150and the virtual long subresonator profiles 152. Each power profile 160 arepresents the power profile of a single temporal pulse of laser output50 that can generally be a sum of the virtual profiles 150 and 152.Skilled persons will appreciate, however, that the virtual profiles 150and 152 may not be entirely additive and that other derivations of thevirtual profiles 150 and 152 may produce power profiles 160. Powerprofile 160 a can be characterized as having a short rise time and along pulse width. Alternatively, power profile 160 a can becharacterized as having two attached spikes with separated peaks. Thepeaks are preferably separated within a time period of from about 15 nsto about 300 ns, so the duration of each pulse may be greater than 300ns.

The short rise times (and to some extent higher peak power) afforded bythe short subresonators sections 36 promote excellent removal of, forexample, most passivation or other layers overlying semiconductor memorylinks and even initiates removal of the links as well in someembodiments. The longer pulse width and lower peak power that arecontributed from the long subresonators 12 help to complete link removalwithout compromising the integrity of the underlying or neighboringsubstrate.

FIGS. 5A-5C (collectively, FIG. 5) show power versus time graphs ofrespective virtual short subresonator profiles 150 and long subresonatorprofiles 152 and exemplary specially tailored profiles 160 b when anexemplary time delay Td₁ is employed.

With reference to FIGS. 2B, 3B, and 5, embodiments such as exemplifiedby lasers 80 b and 110 b that have Q-switches 44 a and 44 b in separatesubresonator sections are well suited for introducing a time delay(generically Td) between the initiation of lasing action of the shortand long subresonators or vice versa. In the exemplary embodiment shownin FIG. 5, Q-switch 44 a in the long subresonator 82 is opened with ashort delay time Td₁ that is shortly after Q-switch 44 b is opened inthe short subresontor 84, to produce the specially tailored profiles 160b. Each power profile 160 b represents the power profile of a singletemporal pulse of laser output 50. As discussed above, the virtualprofiles 150 and 152 may or may not be entirely additive, or otherderivations of them may produce variations of power profile 160 b.

Similarly, FIGS. 6A-6C (collectively, FIG. 6) show respective powerversus time graphs of respective virtual short subresonator profiles 150and long subresonator profiles 152 and exemplary specially tailoredprofiles 160 c when an exemplary long time delay Td₂ is employed. In theexemplary embodiment shown in FIG. 6, Q-switch 44 a in the longsubresonator 82 is opened after a long delay time Td₂ that ends justbefore the lasing action stops in the short subresontor 84, to producethe specially tailored profiles 160 c. Each power profile 160 crepresents the power profile of a single temporal pulse of laser output50. As discussed above, the virtual profiles 150 and 152 may or may notbe entirely additive, or other derivations of them may producevariations of power profile 160 c.

FIGS. 7A-7C (collectively, FIG. 7) show power versus time graphs ofrespective short subresonator profiles 150, long subresonator profiles152, and specially tailored profiles 160 d when an exemplary long timedelay Td₃ is employed. In the exemplary embodiment shown in FIG. 7, AOM44 b in the short subresonator 84 is opened after AOM 44 a with anintermediate delay time Td₃ that substantially centers the spike ofprofile 150 about the spike of profile 152 to produce the speciallytailored profiles 160 b. Each power profile 160 d represents the powerprofile of a single temporal pulse of laser output 50. As discussedabove, the virtual profiles 150 and 152 may or may not be entirelyadditive, or other derivations of them may produce variations of powerprofile 160 d.

With respect to lasers 10, 80 a, and 80 b, the laser profiles 160 of thepulses emitted at the respective output ports are generally inseparableinto their virtual profiles 150 and 152 from the conjoined subresonators(unless polarization elements are employed). Skilled persons willappreciate, however, that the short subresonator profiles 150 and thelong subresonator profiles 152 emerge from separate output ports fromlasers 110 a and 110 b and are subsequently recombined to provide singlepulses of laser output 50 having profiles 160 with high profilestability and pulse-to-pulse consistency.

Alternative embodiments of lasers 110 a and 110 b permit a variety ofunique and useful possibilities for the profiles 160. In one embodiment,the short subresonator profiles 150 are harmonically converted to anultraviolet wavelength (UV) and the long subresonator profiles 152 areharmonically converted to a green wavelength to provide profiles 160having a short rise time in the UV and a long pulse width in the greenwavelength range. In another embodiment, the short subresonator profiles150 are harmonically converted to a 355 nm wavelength and the longresonator profiles 152 remain at a 1064 nm fundamental wavelength toprovide profiles 160 having a short rise time at 355 nm and a long pulsewidth at 1064 nm. In yet another embodiment, a 1.32 μm fundamentalwavelength is employed to produce long subresonator profiles 152 andharmonically doubled (660 nm) or tripled (440 nm) short resonatorprofiles 150 to provide laser output pulses having a short rise time ata purple or blue wavelength and a long pulse width at a 1.32 μmwavelength. The initial small spot size UV short subresonator profiles150 can be used to ablate or rupture the overlying passivation layer andremove part of the link while minimizing crater size and reducing theextent or formation of cracking. Then, the large spot size visible or IRlong subresonator profiles 152 remove the rest of the link, particularlyat a lower than conventional visible or IR output pulse energy or peakpower, with reduced risk of damage to the silicon or other substrate.

Alternatively, the spike of the short resonator profiles 150 could bedelayed to occur somewhere else along the pulse width of the longsubresonator profiles 152. Such delayed spikes might be useful formachining through buried passivation layers, for example. Visible or IRspikes could alternatively be introduced to occur anywhere along thepulse width of a UV long subresonator profile 152 as desired for otherapplications.

The ability to specially tailor pulses to different profile portions atdifferent wavelengths adds extra versatility. The mixing of conventionalIR laser wavelengths and their harmonics for link blowing and otherapplications permits use of a smaller laser beam spot size forprocessing some layers of target and less problematic wavelengths forother layers of the target. New material or dimensions can be employedbecause the profile and duration of laser output 50 can be tailored andreduces the risk of damage to the underlying or neighboring passivationstructure.

Because wavelengths much shorter than about 1.06 μm can be employed toproduce critical spot size diameters of less than about 1.5 μm, thecenter-to-center pitch between the links processed with laser output 50can be substantially smaller than the pitch between links blown by aconventional single IR laser beam-severing pulse. Therefore, theprocessing of narrower and denser links could be facilitated, resultingin better link removal resolution, permitting the links to be positionedcloser together, and increasing circuit density.

Similarly, the versatility of better tailoring the laser pulse powerprofile 160 offers better flexibility in accommodating different or morecomplicated passivation characteristics. For example, the passivationlayers above or below the links can be made with material other than thetraditional materials or can be modified, if desired to be other than atypical height.

The overlying passivation layer may include any conventional passivationmaterials such as silicon dioxide (SiO₂), silicon oxynitride (SiON), andsilicon nitride (Si₃N₄). The underlying passivation layer may includethe same passivation material as or different passivation material(s)from overlying passivation layer. In particular, the underlyingpassivation layer in the target structures may be formed from fragilematerials, including but not limited to, materials formed from low Kmaterials, low K dielectric materials, low K oxide-based dielectricmaterials, orthosilicate glasses (OSGs), fluorosilicate glasses,organosilicate glasses, a tetraethylorthosilicate-based oxide(TEOS-based oxide), methyltriethoxyorthosilicate (MTEOS), propyleneglycol monomethyl ether acetate (PGMEA), silicate esters, hydrogensilsesquioxane (HSQ), methyl silsesquioxane (MSQ), polyarylene ethers,benzocyclobutene (BCB), SiCOH or SiCOH-derived film (such as “BlackDiamond” sold by Applied Materials, Inc.), or spin on-based low Kdielectric polymer (such as “SiLK” sold by Dow Chemical Company). Theunderlying passivation layers made from some of these materials are moreprone to crack when their targeted links are blown or ablated byconventionally shaped laser pulse link-removal operations. Skilledpersons will appreciate that SiO₂, SiON, Si₃N₄, low K materials, low Kdielectric materials, low K. oxide-based dielectric materials, OSGs,fluorosilicate glasses, organosilicate glasses, HSQ, MSQ, BCB, SiLK™,and Black Diamond™ are actual layer materials, and TEOS, MTEOS, andpolyarylene ethers are semiconductor condensate precursor materials.Even though some of the newer overlying passivation layers could be lessreceptive to conventional laser processing and/or some of the underlyingpassivation layers could be more sensitive with respect to conventionallaser processing, the techniques described herein often greaterversatility when dealing with layers with different properties.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

1. A method for controlling the temporal energy profile characteristicsof laser output pulses, comprising: employing a first subresonator witha first subresonator length that imparts a rise time characteristic to afirst subresonator pulse profile in response to lasing pulse initiation,the first subresonator having a first subresonator section with a firstsubresonator section length that contributes to the first subresonatorlength; employing a second subresonator with a second subresonatorlength that imparts a pulse width characteristic to second subresonatorpulse profile in response to lasing pulse initiation, the secondsubresonator having a second subresonator section with a secondsubresonator section length that contributes to the second subresonatorlength, and the second subresonator length being longer than the firstsubresonator length; employing a common resonator subsection that isshared by the first and second subresonators to cause thecharacteristics imparted from the first and second subresonator pulseprofiles to be expressed during a lasing pulse, the common resonatorsubsection having a length that contributes to both the firstsubresonator length and the second subresonator length; initiating thelasing pulse to express the characteristics imparted from the first andsecond subresonator pulse profiles; and emitting a laser output pulsehaving the rise time characteristic imparted from the first subresonatorand the pulse width characteristic imparted from the secondsubresonator.
 2. The method of claim 1 in which the first subresonatorhas a short first subresonator length that imparts a short rise time tothe laser output pulse and the second subresonator has a long secondsubresonator length that imparts a long pulse width to the laser outputpulse so that the laser output pulse exhibits a short rise time and along pulse width.
 3. The method of claim 1 in which the laser outputpulse exhibits a rise time that is shorter than 8 ns and a pulse widththat is longer than 10 ns.
 4. The method of claim in which the laseroutput pulse exhibits two separated peaks within a time period of from15 ns to 300 ns.
 5. The method of claim 1 in which a beam splitter isemployed to integrate the first and second subresonators.
 6. The methodof claim 1 in which a polarizer is employed to integrate the first andsecond subresonators.
 7. The method of claim 1 in which the commonresonator subsection includes a Q-switch.
 8. The method of claim 1 inwhich each of the first and second subresonator sections comprises aQ-switch.
 9. The method of claim 1 in which the common resonatorsubsection includes a solid-state laser medium.
 10. The method of claim1 in which the common resonator subsection comprises a highly reflectivemirror and the first and second subresonator sections each have anoutput port.
 11. The method of claim 1 in which the laser output pulseis converted to a different wavelength by use of an extra-cavitywavelength converter.
 12. The method of claim 1 in which the commonresonator subsection comprises one or more wavelength converters. 13.The method of claim 1 in which the initiation of the first and secondsubresonator pulse profiles is substantially simultaneous.
 14. Themethod of claim 1 in which laser output pulses are generated at arepetition rate of greater than 1 kHz.
 15. The method of claim 1 inwhich laser output pulses are generated at a repetition rate of greaterthan 40 kHz.
 16. The method of claim 1 in which a time delay isintroduced between initiation of the first and second subresonator pulseprofiles.
 17. The method of claim 16 in which the time delay is shorterthan 300 ns.
 18. The method of claim 16 in which the time delay endsjust before lasing pulse action stops in the subresonator that is firstinitiated.
 19. The method of claim 1 in which the first and secondsubresonator sections each include a solid-state laser medium.
 20. Themethod of claim 19 in which the solid-state laser media of the first andsecond subresonator sections comprise the same lasant material.
 21. Themethod of claim 19 in which the solid-state laser media of the first andsecond subresonator sections comprise different lasant materials thatemit at a substantially similar wavelength.
 22. The method of 21 inwhich the solid-state laser media of the first subresonator sectioncomprises Nd:YVO, and the solid-state laser media of the secondsubresonator section comprises Nd:YAG.
 23. The method of claim 19 inwhich the solid-state laser media of the first and second subresonatorsections have different dimensions.
 24. The method of claim 19 in whichthe solid-state laser media of the first and second subresonatorsections have dimensions that are about the same.
 25. The method ofclaim 19 in which the first and second subresonator sections eachcomprise one or more wavelength converters.
 26. The method of claim 19in which the solid-state laser media of the first and secondsubresonator sections are pumped at different levels.
 27. The method ofclaim 19 in which the solid-state laser media of the first and secondsubresonator sections are pumped at levels that are about the same. 28.The method of claim 19 in which pumping is initiated for the solid-statelaser media of the first and second subresonator sections at differenttimes.
 29. The method of claim 19 in which pumping is initiated for thesolid-state laser media of the first and second subresonator sections atabout the same time.
 30. The method of claim 19 in which the solid-statelaser media of the first and second subresonator sections have differentshapes.
 31. The method of claim 19 in which the solid state laser mediaare CW pumped.
 32. The method of claim 1 in which the common resonatorsubsection includes a common output port from which the laser outputpulse is emitted.
 33. The method of claim 32 in which the laser outputpulse has a temporal energy profile that is inseparable into the pulseprofiles of the first and second subresonators.
 34. The method of claim32 in which the common output port comprises an output coupling mirror.35. The method of claim 1 in which each of the first and secondsubresonator sections has its own output port.
 36. The method of claim35 in which each of the first and second subresonator sections includesa wavelength converter.
 37. The method of claim 35 in which the firstsubresonator pulse profile and the second subresonator pulse profilepropagating from the respective output ports of the first and secondsubresonator sections are combined along a common optical path toprovide the laser output pulse.
 38. The method of claim 37 in which afirst emission from the first subresonator section and/or a secondemission from the second subresonator section is converted to adifferent wavelength such that the first and second emissions combinedalong the optical path include at least two wavelengths.
 39. The methodof claim 37 in which a first emission from the first subresonatorsection and/or a second emission from the second subresonator sectionhave different spot size characterisitics.
 40. The method of claim 37 inwhich the initiation of the first and second subresonator pulse profilesis substantially simultaneous.
 41. The method of claim 37 in which atime delay is introduced between initiation of the first and secondsubresonator pulse profiles.
 42. The method of claim 37 in which thefirst and second subresonator pulse profiles express their spikes atsubstantially the same time.
 43. The method of claim 37 in which laseroutput pulses are propagated at a repetition rate of greater than 40kHz.
 44. The method of claim 37 in which the laser output pulse has anoutput profile with a visible- or UV-wavelength spike and an IR tail.45. The method of claim 44 in which the IR tail comprises a wavelengthof one of about 1.047, 1.054, 1.064, or 1.32 microns.
 46. The method ofclaim 1 in which the laser output pulse is employed to sever a linkon-the-fly.
 47. A method for generating a laser output pulse having alaser output pulse pulse profile that includes at least two wavelengths,comprising: employing a common resonator subsection having a commonresonator subsection length along a common optical path; employing abeam splitter positioned to intersect the common optical path; employinga first subresonator section including a first subresonator path thatintersects the common optical path in proximity to the beam splitter,the first subresonator section having a first subresonator sectionlength, the first subresonator section and the common resonatorsubsection forming a first subresontaor having a first subresonatorlength that includes the first subresonator section length and thecommon resonator subsection length, and the first subresonator lengthimparting to each laser pulse a first spike characteristic and a firstpulse width characteristic; employing a second subresonator sectionincluding a second subresonator path that intersects the common opticalpath in proximity to the beam splitter, the second subresonator sectionhaving a second subresonator section length, the second subresonatorsection and the common resonator subsection forming a secondsubresonator having a second subresonator length that includes thesecond subresonator section length and the common resonator subsectionlength, the second subresonator length imparting to each laser pulse asecond spike characteristic and a second pulse width characteristic, andthe second subresonator length being longer than the first subresonatorlength; employing first and second solid-state laser media positioned inthe respective first and second subresonator sections for receivinglaser pumping light from one or more laser pumping sources, the firstand second laser media being adapted to facilitate lasing action at afundamental wavelength, wherein the common resonator section links thelasing action in the first subresonator with the lasing action in thesecond subresonator to cause propagation of a laser pulse that exhibitsat least the first spike characteristic imparted from the firstsubresonator and the second pulse width characteristic imparted from thesecond subresonator; employing a first output port from the firstsubresonator section and a second output port from the secondsubresonator section to split each laser pulse into to first laseroutput that propagates through the first output port and second laseroutput that propagates through the second output port, the first laseroutput exhibiting the first spike and pulse width characteristics andthe second laser output exhibiting the second spike and second pulsewidth characteristics; employing a first wavelength converter positionedalong a first beam path from the first output port to convert the firstlaser output to a first wavelength and/or employing a second wavelengthconverter positioned along a second beam path from the second outputport to convert the second laser output to a second wavelength; andcombining the first laser output with the second laser output to providea laser output pulse having at least first spike characteristics at thefundamental or first wavelength and having at least second pulse widthcharacteristics at the fundamental or second wavelength such that thelaser output pulse exhibits at least two distinct wavelengths.
 48. Amethod for controlling the temporal energy profile and/or pulse widthcharacteristics of a laser output pulse, comprising: employing a firstsubresonator with a first design feature that imparts a first energyprofile and/or pulse width characteristic to each laser pulse; employinga second subresonator with a second design feature that imparts a secondenergy profile and/or pulse width characteristic to each laser pulse,the first and second design features imparting different characteristicsto the pulses of laser output; employing a common resonator subsectionthat is shared by the first and second subresonators to couple lasingaction in the first and second subresonators; and directing at a targeta laser output pulse having laser output energy profile and/or pulsewidth characteristics derived from the first and second energy profileand/or pulse width characteristics.
 49. The method of claim 48 in whicha beam splitter is employed to integrate the first and secondsubresonators.
 50. The method of claim 48 in which the firstsubresonator has a length that is shorter than the second subresonatorsuch that the first subresonator imparts a short rising edge to thepulses of laser output and the second subresonator imparts a long pulsewidth to the pulses of laser output so that the laser output pulsesexhibit a short rising edge and a long pulse width.
 51. The method ofclaim 48 in which the common resonator subsection includes a Q-switch.52. The method of claim 48 in which the common resonator subsectionprovides a common output port for the laser output pulses.
 53. Themethod of claim 48 in which the common resonator subsection includes asolid-state laser medium.
 54. The method of claim 48 in which the firstand second subresonators each include a solid-state laser medium and aQ-switch.
 55. The method of claim 48 in which the pulses of laser outputare converted to a different wavelength by use of an extra-cavitywavelength converter.
 56. The method of claim 48 in which the commonresonator subsection comprises a highly reflective mirror and the firstand second subresonators each have an output port.